This application claims the priority of Austrian Patent Application, Serial No. A 621/2001, filed Apr. 17, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a temperature limiter.
Typically, temperature limiters, involved here, include a switch head with a switching contact, and a temperature sensor in the form of elongate expansion elements which have different thermal expansion coefficients and are defined by a switch head distal end zone in which the expansion elements are fixed immobile relative to one another, and a switch head proximal end zone in which one of the expansion elements is movable relative to the other expansion element. A ram is slidably supported in the switch head and abuts against the movable expansion element, whereby the ram has an end portion which is operatively connected to the switching contact.
The response temperature at which the switching contact is actuated by the ram is dependent on the distance between the switching contact and the ram part that actually acts on the switching contact. Therefore, this distance must be adjusted to set the response temperature. The adjustment can be implemented by manufacturing the ram with precise dimensions or by mechanical finishing the ram, e.g., precision cutting, grinding or the like. This approach is disadvantageous because the finishing process can be carried out only when the temperature limiter is disassembled. As a result, the ram has to be removed from the switch head in order to carry out finishing works. Needless to say that the calibration of the response temperature is complicated and inefficient.
Conventional calibration devices are known which include a switch sleeve placed over the end portion of the ram for actuation of the switching contact. The switch sleeve has an internal thread for threaded engagement of a stud bolt which rests with one end face against the ram. Thus, turning the stud bolt results in a displacement of the switch sleeve relative to the ram to thereby allow adjustment of the response temperature of the switching contact. This approach is also disadvantageous because the use of the stud bolt is inaccurate as even slight turns of the stud bolt are accompanied by a relatively substantial displacement of the switch sleeve. A fine-tuned calibration becomes thus impossible. Further, the stud bolt is prone to self-turning during the course of time, especially because of the exposure to frequent temperature changes and to frequent displacement forces. These turns of the stud bolt lead necessarily to an alteration of the set response temperature.
It would therefore be desirable and advantageous to provide an improved temperature limiter which obviates prior art shortcomings and which is configured to enable simple calibration of the response temperature of the switch contact in a very accurate manner.
According to one aspect of the present invention, a temperature limiter, includes a switch head including at least one switching contact; a temperature sensor including elongate expansion elements which have different thermal expansion coefficients and are defined by a switch head distal first end zone at which the expansion elements are fixed immobile relative to one another, and a switch head proximal second end zone at which one of the expansion elements is movable relative to the other expansion element; a ram slidably supported in the switch head and abutting against the movable expansion element, with the ram having an end portion which is situated in an area of the switching contact and constructed to allow application of a welding or soldering process; and a switch sleeve placed over the end portion of the ram and adapted for actuation of the switching contact, wherein the switch sleeve is movable relative to the ram during a calibration phase, until reaching a position which is determinative for calibrating a desired response temperature of the switching contact and in which position the switch sleeve is securely fixed to the end portion of the ram through a process selected from the group consisting of fusion welding and soldering.
In a temperature limiter according to the present invention, the switch sleeve can be shifted very precisely even over small distances into the desired position where the switch sleeve is then permanently secured to the ram through welding or soldering. Inadvertent shifts of the switch sleeve and resulting alterations of the set response temperature are effectively eliminated, once the calibration has been implemented.
According to another feature of the present invention, the switch sleeve may be connected to the end portion by laser welding or laser soldering. Such a connection can be established easily, when the temperature limiter is fully assembled because the laser beam utilized for heating the parts being welded or soldered together requires only little space.
According to another feature of the present invention, the switch sleeve may be provided with a gripping aid, e.g., in the form of a pin or in the form of indentations in or roughening of an outer surface area of the switch sleeve. In this way, application of forces required to shift the switch sleeve is substantially facilitated.
According to another feature of the present invention, there may be provided a spring, e.g., a helical compression spring, for loading the switch sleeve to seek a position away from an end face of the end portion of the ram. The displacement of the switch sleeve is hereby considerably facilitated in a simple manner, because only one force is required to act upon the switch sleeve to effect a displacement of the switch sleeve in the direction of the end face of the ram, while the return of the switch sleeve in the other direction is realized automatically by the spring. As a consequence, the displacement of the switch sleeve requires only an outside force onto the switch sleeve end face that is distal to the end face of the ram. This can easily be realized through a respective opening in the adjacent sidewall of the switch head. Moreover, as the switch sleeve is moved in the direction of the end face of the ram in opposition to a resistance applied by the spring force, the calibration is fine-tuned and more exact compared to a situation in which an unbiased structural part is displaced. The response temperature can thus be set very accurately.
According to another feature of the present invention, a metal film may be applied onto the end portion of the ram so that the switch sleeve can be directly welded to the ram. There is no need to provide additional components to implement the connection between the switch sleeve and the ram.
According to another feature of the present invention, there may also be applied a coat of solder onto the metal film. In this way, a soldered connection can be realized between the switch sleeve and the metal film on the end portion of the ram through suitably heating the switch sleeve. Supply of solder is not required as the coat of solder has already been deposited on the metal film.
According to another feature of the present invention, there may be provided a receiving sleeve which is placed over the end portion of the ram and connected to the end portion, wherein the switch sleeve is placed over the receiving sleeve. Production and attachment of such a receiving sleeve is overall more economical compared to metallization of the ram end portion and requires only simple and cost-efficient welding or soldering operation for connection of the receiving sleeve to the ram end portion.
According to another feature of the present invention, the receiving sleeve may have an abutment at a location distant to a confronting end face of the switch sleeve, wherein a helical compression spring is arranged between the abutment and the confronting end face of the switch sleeve, for loading the switch sleeve to seek a position away from the end face of the ram end portion. In this way, all components used for implementing the adjustment of the response temperature form a compact unit which can be pre-assembled and then attached to the ram.